After much faffing about, this worked for me, but it's a bit long winded:
1) I downloaded the files from the Wessex SR website on to my PC 'downloads' folder.
2) I then uploaded all 7 files/routes in to Ride With GPS
3) I changed the route names to Portkers 1, Porkers 2, Porkers 3 etc in Ride With GPS
4) I then exported the files as GPX files from Ride With GPS to my PC 'downloads' folder
5) I copied the files to my Garmin
I suspect that steps 4 and 5 could be done as one, ie directly to the Garmin, but that's not what I did.
When I changed the file names in the Downloads folder, I couldn't get more than one file to register on my Garmin, which is why I did the name changes in Ride With GPS. It seemed to me that the problem with the original versions is that they all seemed to have the same name as far as the Garmin was concerned, so the Garmin only registered one....that may not be the case, but that's what it seemed like to me and the fact that it only worked after doing the name changes in Ride With GPS clinches the argument for me!